1. Field of the Invention
The present invention relates generally to labyrinth seals and concerns, more particularly, improvements for labyrinth seals that separate two spaces containing fluids at different pressures and which comprise small fins in rapid motion with respect to elements of the seal that operate in conjunction with them, such as, for example, a seal placed between a shaft and the combustion chamber housing of a gas turbine or of an aviation turbojet.
2. Description of the Prior Art
Such a seal as characterized herein separates an upstream space, which contains air at the exhaust pressure of the last compression stage of the turbojet or of the gas turbine set, such as 20 bar at full load, from a downstream space which connects to the first mobile turbine blading, at a pressure such as 10 bar, for example. The efficiency of the turbine is highly sensitive, however, to the rate of flow of the air input at its first blading (for example, introduction of such an air flow that is equal to 1% of the air expelled by the compressor can cause a 1.5% reduction in the turbine output). It is therefore essential that the labyrinth seal be highly efficacious, i.e., that the clearance between the fins and the corresponding elements of the seal be kept very small, which requires a very precise adjustment of their relative shift during the operation of the turbo-engine.
The main cause of deformation is of thermal origin. In fact, it has been observed that the elements of the seal, which operate in conjunction with the fins, heat up during the operation and tend to dilate more downstream than upstream. This is a fairly unexpected phenomenon, for one would rather expect that the air expansion at passage through the seal might produce a cooling effect. One explanation of this phenomenon is that the air is heated by the stirring and lamination between the fins and the corresponding elements of the seal as the air flows downstream. It goes without saying, however, that the invention is in no way limited by scientific hypotheses or explanations.